A conventionally known open type rubber kneading machine is generally a twin-roll machine. The twin-roll machine is disposed such that two roll shafts are parallel in a horizontal-plane and their rolling surfaces are close to each other. Raw material rubber is fed between rolls from above while rotatively driving the two rolls. The two rolls are rotated at different speeds while being pressed into contact so as to apply shearing action to the rubber, thereby imparting plasticizing and grinding effect. An operator manually cuts apart the rubber wound around the rolls on the operating side by a cutter and winds it up or moves it to one side of the rolls by hand so as to facilitate mixing in a batch. This is because merely applying the shearing force to the rubber wound on the rolls results in uneven kneading action in the batch.
Thus, in the aforesaid publicly known rubber kneading machine, it is possible to accomplish even mixing of rubber in a batch by cutting rubber on a pair of rolls that are horizontally and closely disposed and rotated. For an operator, however, it is unsafe to work on rubber, which unavoidably includes contact with rotating rolls. The operation involves great danger, frequently causing serious injuries of operators by getting their hands or fingers caught between the rolls.
Recently, a sheeting apparatus combining an extruder and rolls is being put to practical use to replace the aforesaid roll machine. In this apparatus, a pair of rolls is vertically disposed, and the outlet of a screw extruder is disposed closely to the rolls so as to roll rubber into a rubber sheet by the pair of rolls. This apparatus, however, merely has a function for pushing kneaded rubber into the rolls from the screw extruder to form it into a sheet by one passage through the rolls. It has been ascertained that effect of finish kneading or mixing a vulcanizing agent cannot be obtained even when a circulation belt conveyor is provided to perform circulation kneading. In a process requiring such an operation, another twin-roll machine must be installed.
As may be understood from the description above, a rubber kneading machine is required to ensure efficient kneading operation and safety. In the aforesaid twin-roll rubber kneading machine, the quality of kneaded rubber depends on kneading action and skill of individual operators. The operators manually cut loose or wind up rubber wound around the surfaces of rotating rolls. This operation is not only painstaking but extremely dangerous.
Hence, there has been a demand for making it possible to mechanically perform the operation requiring skill without human aid. No equipment capable of performing such an operation has been developed. If production equipment performing such a rubber kneading operation is developed, then it will be possible to relieve fatigue, ensure safety, and secure uniform quality by standardizing operations.
On the other hand, if a rubber kneading machine is constructed to provide efficient kneading operation and high safety required by users, then the closeness of the rubber kneading machine itself is enhanced. This would require time-consuming cleaning of the interior of the rubber kneading machine to prevent a different material from being mixed in whenever a rubber with a different composition is used. In addition, the construction would make it difficult to perform thorough visual check after cleaning.
In this respect, the conventional open type rubber kneading machine permits relatively easy cleaning, whereas it markedly lacks in safety measures for operators, since it is an open type. In the aforesaid sheeting apparatus, rolls are moved to provide a gap between a distal end of a screw and the rolls, and the rolls are moved far apart so as to scrape out remaining material from an extrusion cylinder of the screw extruder, or a hopper at the top of a proximal end of a screw is opened to inspect and clean the interior of the extrusion cylinder. It is difficult, however, to thoroughly clean the interior of the extrusion cylinder and to fully check cleaning results, because of the presence of two screws. Especially for colored food or rubber dough for pharmaceuticals, it is necessary to carry out thorough cleaning to prevent any different materials from being mixed in whenever a different color or composition is used. Hence, there has been a demand for a rubber kneading machine that permits easy cleaning of closed parts and checking of cleaning results while maintaining efficient kneading operation and high safety.